1. [Field of the Invention]
This invention relates to an inclined magnetic field generator for use in a magnetic resonance diagnostic apparatus for medical use.
2. [Description of the Prior Art]
FIG. 5 is a structural diagram showing conceptually the entire configuration of a magnetic resonance diagnostic apparatus disclosed in Japanese Patent Publication No. 3173530, for example.
In FIG. 5, reference numeral 1 represents a magnet for generating a magnetostatic field in an inner space 2. Numeral 3 represents a subject who is accommodated in the magnetostatic field while lying on the bed 4, for example. Numeral 5 represents an irradiation coil disposed around the subject 3. Numeral 6 denotes an inclined magnetic field generator to which a drive current for excitation is supplied from an inclined magnetic field power source 7 and which is provided around the outside of the irradiation coil 5 to generate inclined magnetic fields in X, Y and Z axes which cross one another at a right angle. Numeral 8 represents a receiving Coil arranged near the head of the subject 3. Numeral 9 represents a transmitter connected to the irradiation coil 5, for supplying a high frequency signal for generating a high-frequency magnetic field so as to obtain a magnetic resonance signal.
Due to a function of a magnetostatic field, inclined magnetic field and high-frequency magnetic field, a magnetic resonance signal is generated from the subject 3. This magnetic resonance signal is detected by the receiving coil 8, and the signal received by a receiver 10 is processed by a data processor 11 to reproduce an image. As a result, the obtained data is displayed on a CRT display 12 as an image to be inspected.
Numeral 13 represents a controller for supplying a control signal to the inclined magnetic field power source 7, transmitter 9 and receiver 10 to control their operation contents and timings.
FIG. 6 is a front view of the main coils and shielding coils of an inclined magnetic field generator. FIG. 7 is a side view of FIG. 6.
In FIG. 6 and FIG. 7, a total of four coils 15 for the X axis, that is, two pairs of opposing coils 15 are disposed over a cylindrical bobbin 14, and a total of four coils 16 for the Y axis, that is, two pairs of opposing coils 16 are also disposed over the cylindrical bobbin 14. The coils 15 and 16 are all shaped like a saddle. Further, two coils 17 for the Z axis, not in a pair, are wound around the bobbin 14.
In FIG. 7, arrows provided in each of the coils 15, 16 and 17 indicate the directions of currents at an arbitrary moment which are concurrent with one another.
FIG. 8 is a development of conventional coils for the X and Y axes formed like a saddle by winding a conductor spirally and developed on a plane.
In FIG. 8, numeral 18 represents a spiral coil which is arranged to have a fixed width of a conductor 18a with the width of a groove 19 in the conductor 18a changing depending on the shape of the coil.
The coil 18 is formed by cutting and removing in a longitudinal direction both sides of the conductor 18a from a plate-form conductive member by water jet cutting or other technique.
FIG. 9 is a diagram showing the state of the coil when it is cut on a line IX--IX. In FIG. 9, numerals 20 and 21 represent cut grooves produced by water jet cutting, and 22 a waste material cut away for forming the groove 19 in the conductor 18a.
FIG. 10 is a structural diagram showing a combination of main coils and shielding coils for shielding magnetic field leakage to the outside. FIG. 11 is a sectional view of FIG. 10 cut on a line XI--XI.
In FIG. 10 and FIG. 11, numeral 23 represents main coils wound around the bobbin 14 over which the coils 15, 16 and 17 are disposed as shown in FIG. 7. Numeral 24 represents shielding coils for shielding magnetic field leakage from the main coils 23 to the outside, which consist of a coil 24a for the X axis, a coil 24b for the Y axis and a coil 24c for the Z axis, all wound around a bobbin 25 which is provided around the main coils 23 with a predetermined space therebetween. Numeral 26 represents a fixing tool or spacer provided between the bobbins 14 and 25, for fixing the relative positions of the coils 23 and 24 electrically and mechanically.
In the above configuration, the main coils 23 for generating a main inclined magnetic field are installed at a predetermined position of the bobbin 14, and are fixed to withstand electromagnetic mechanical forces which work at the time of operation in directions indicated by arrows 27.
Like the main coils 23, the shielding coils 24 are installed at a predetermined position of the bobbin 25, and are fixed to withstand electromagnetic mechanical forces which work at the time of operation in directions indicated by the arrows 27. The electromagnetic mechanical forces applied to the main coils 23 and the shielding coils 24 are opposite to each other in direction, but the same in phase, and are supported or borne by the bobbins 14 and 25, respectively. The coils 23 and 24 are fixed at predetermined relative positions by the fixing tool 26 to generate an inclined magnetic field.
Since the inclined magnetic field generator of the prior art is constructed as described above, both sides of the conductor must be cut along the entire length thereof. Therefore, the prior art has the problem of requiring a long time for cutting, due to a long length needed to be cut. In addition, it has another problem that a large amount of waste material is produced because a groove needs to be formed in the conductor.
Further, it involves the problem that the bobbin must be built rigid enough to prevent vibration and noise because it receives the electromagnetic mechanical force of the shielding coils.
Moreover, it involves another problem of insufficient cooling effect as the shielding coils are cooled through the bobbin when air is passed between the main coils and the shielding coils for forced cooling.